This invention relates to the electrolytic oxidation of appropriately substituted cresol salts to produce the corresponding methyl-methyl coupled dehydrodimeric cresols. More particularly, this invention relates to the electrolytic oxidative methyl-methyl coupling of cresol salts substituted with non-interfering, blocking substituents at least at the 2,4,6-positions relative to the phenolic oxyanion where at least one of the substituents is the cresolic methyl to produce methyl-methyl coupled dehydrodimeric cresol, or simply 1,2-bis(hydroxyaryl)ethanes.
Oxidative methyl-methyl coupling of cresols has previously been accomplished, particularly to prepare the corresponding 1,2-bis(hydroxyaryl)ethanes, by the use of a variety of oxidizing agents. For example, oxidizing agents such as alkaline potassium hexacyanoferrate (III), lead (IV) oxide, silver oxide, air in cumene containing iron (III) stearate, air in chlorobenzene containing 2,2'-azobis(2-methylpropanenitrile)(.alpha.,.alpha.'-azobisisobutyronitril e), organic peroxides, and the like have been used for this purpose. Each of these known reagents has certain disadvantages when used in this reaction. These may include low yield, simultaneous production of contaminating by-products such as stilbenequinone structures, and the necessity of using extremely dilute solutions and long reaction periods. Moreover, some of the reagents are relatively expensive.
The disadvantages encountered in the prior art chemical oxidative methyl-methyl coupling processes are overcome by the discovery that appropriately substituted cresol salts undergo electrolytic oxidation to produce methyl-methyl coupled dehydrodimeric cresols (1,2-bis(hydroxyaryl)ethanes).